On the Synthesis and Structure of 'Naked' Ga(I) and In(I) Salts and the Surprising Stability of Simple Ga(I) and In(I) Salts in the Coordinating Solvents Ether and Acetonitrile.

In this work, we present the solid-state structures of solvent-free Ga[pf] and In[pf] salts ([pf]-=[Al(ORF)4]-; RF=C(CF3)3), which are very rare examples of salts with truly 'naked' metal cations. Both salts may serve as starting materials for subvalent gallium and indium chemistry with very weakly coordinating ligands providing the freedom of choice for solvents and ligands for the future. On the other hand, we report and rationalize the formation and isolation of [M(OEt2)2][pf] and [M(MeCN)2][pf] (M=Ga, In), underlining the surprising stability of these subvalent group 13 M+ ions against disproportionation. Unexpectedly, dicoordinate and carbene analogous [M(L)2]+ ions with the [pf]- counterion are stable in L=acetonitrile and diethyl ether at room temperature, opening up possible applications for example in organic synthesis and catalysis.

Structures, Bonding Analyses and Reactivity of a Dicationic Digallene and Diindene Mimicking trans-bent Ditetrylenes.

The reaction of bisdicyclohexylphosphinoethane (dcpe) and the subvalent MI sources [MI (PhF)2 ][pf] (M=Ga+ , In+ ; [pf]- =[Al(ORF )4 ]- ; RF =C(CF3 )3 ) yielded the salts [{M(dcpe)}2 ][pf]2 , containing the first dicationic, trans-bent digallene and diindene structures reported so far. The non-classical MI ⇆MI double bonds are surprisingly short and display a ditetrylene-like structure. The bonding situation was extensively analyzed by quantum chemical calculations, QTAIM (Quantum Theory of Atoms in Molecules) and EDA-NOCV (Energy Decomposition Analysis with the combination of Natural Orbitals for Chemical Valence) analyses and is compared to that in the isoelectronic and isostructural, but neutral digermenes and distannenes. The dissolved [{Ga(dcpe)}2 ]2+ ([pf]- )2 readily reacts with 1-hexene, cyclooctyne, diphenyldisulfide, diphenylphosphine and under mild conditions at room temperature. This reactivity is analyzed and rationalized.

Direct Comparison of Subvalent, Polycationic Group 13 Cluster Compounds: Lessons learned on Isoelectronic DMPE Substituted Gallium and Indium Tetracation Salts.

The tetracationic, univalent cluster compounds [{M(dmpe)}4 ]4+ (M=Ga, In; dmpe=bis(dimethylphosphino)ethane) were synthesized as their pf salts ([pf]- =[Al(ORF )4 ]- ; RF =C(CF3 )3 ). The four-membered ring in [{M(dmpe)}4 ]4+ is slightly puckered for M=Ga and almost square planar for M=In. Yet, although structurally similar, only the gallium cluster is prevalent in solution, while the indium cluster forms temperature dependent equilibria that include even the monomeric cation [In(dmpe)]+ . This system is the first report of one and the same ligand inducing formation of isoelectronic and isostructural gallium/indium cluster cations. The system allows to study systematically analogies and differences with thermodynamic considerations and bonding analyses, but also to outline perspectives for bond activation using cationic, subvalent group 13 clusters.

Phenyl-Group Exchange in Triphenylphosphine Mediated by Cationic Gold-Platinum Complexes-A Gas-Phase Mimetic Approach.

The PPh3 ligands in the heterodinuclear AuPt complex [(Ph3P)AuPt(PPh3)3][BAr4F] (BAr4F = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) exhibit a high fluxionality on the AuPt core. Fast intramolecular and slow intermolecular processes for the reversible exchange of the PPh3 ligands have been identified. When [(Ph3P)AuPt(PPh3)3][BAr4F] is heated in solution, the formation of benzene is observed, and a trinuclear, cationic AuPt2 complex is generated. This process is preceded by reversible phenyl-group exchange between the PPh3 ligands present in the reaction mixture as elucidated by deuterium-labeling studies. Both the elimination of benzene and the preceding reversible phenyl-group exchange have originally been observed in mass-spectrometry-based CID experiments (CID = Collision-Induced Dissociation). While CID of mass-selected [Au,Pt,(PPh3)4]+ results exclusively in the loss of PPh3, the resulting cation [Au,Pt,(PPh3)3]+ selectively eliminates C6H6. Thus, the dissociation of a PPh3 ligand from [Au,Pt,(PPh3)3]+ is energetically not able to compete with processes which result in C-H- and C-P-bond cleavage. In both media, the heterobimetallic nature of the employed complexes is the key for the observed reactivity. Only the intimate interplay of the gas-phase investigations, studies in solution, and thorough DFT computations allowed for the elucidation of the mechanistic details of the reactivity of [(Ph3P)AuPt(PPh3)3][BAr4F].

A Highly Lewis Acidic Strontium ansa-Arene Complex for Lewis Acid Catalysis and Isobutylene Polymerization.

The potential of a dicationic strontium ansa-arene complex for Lewis acid catalysis has been explored. The key to its synthesis was a simple salt metathesis from SrI2 and 2 Ag[Al(ORF )4 ], giving the base-free strontium-perfluoroalkoxyaluminate Sr[Al(ORF )4 ]2 (ORF =OC(CF3 )3 ). Addition of an ansa-arene yielded the highly Lewis acidic, dicationic strontium ansa-arene complex. In preliminary experiments, the complex was successfully applied as a catalyst in CO2 -reduction to CH4 and a surprisingly controlled isobutylene polymerization reaction.

Coordination Chemistry of P4 S3 and P4 Se3 towards the Iron Fragments [Fe(Cp)(CO)2 ]+ and [Fe(Cp)(PPh3 )(CO)].

The complexes Ag(L)n [WCA] (L=P4 S3 , P4 Se3 , As4 S3 , and As4 S4 ; [WCA]=[Al(ORF )4 ]- and [F{Al(ORF )3 }2 ]- ; RF =C(CF3 )3 ; WCA=weakly coordinating anion) were tested for their performance as ligand-transfer reagents to transfer the poorly soluble nortricyclane cages P4 S3 , P4 Se3 , and As4 S3 as well as realgar As4 S4 to different transition-metal fragments. As4 S4 and As4 S3 with the poorest solubility did not yield complexes. However, the more soluble silver-coordinated P4 S3 and P4 Se3 cages were transferred to the electron-poor Fp+ moiety ([CpFe(CO)2 ]+ ). Thus, reaction of the silver salt in the presence of the ligand with Fp-Br yielded [Fp-P4 S3 ][Al(ORF )4 ] (1 a), [Fp-P4 S3 ][F(Al(ORF )3 )2 ] (1 b), and [Fp-P4 Se3 ][Al(ORF )4 ] (2). Reactions with P4 S3 also yielded [FpPPh3 -P4 S3 ][Al(ORF )4 ] (3), a complex with the more electron-rich monophosphine-substituted Fp+ analogue [FpPPh3 ]+ ([CpFe(PPh3 )(CO)]+ ). All complex salts were characterized by single-crystal XRD, NMR, Raman, and IR spectroscopy. Interestingly, they show characteristic blueshifts of the vibrational modes of the cage, as well as structural contractions of the cages upon coordination to the Fp/FpPPh3 moieties, which oppose the typically observed cage expansions that lead to redshifts in the spectra. Structure, bonding, and thermodynamics were investigated by DFT calculations, which support the observed cage contractions. Its reason is assigned to σ and π donation from the slightly P-P and P-E antibonding P4 E3 -cage HOMO (e symmetry) to the metal acceptor fragment.

From Phosphidic to Phosphonium? Umpolung of the P4 -Bonding Situation in [CpFe(CO)(L)(η1 -P4 )]+ Cations (L=CO or PPh3 ).

Upon coordinating P4 to electron poor cyclopentadienyl-iron cations, the average P-P bond distances shrink and the respective P4 breathing mode in the Raman spectra (600 cm-1 , P4, free ) is blueshifted by >40 cm-1 in [CpFe(CO)(L)(η1 -P4 )]+ cations (L=CO or PPh3 ). Analysis suggests that this corresponds to an umpolung of the bonding from more phosphidic in the known, electron-rich systems to more phosphonium-like in the reported electron-poor versions. This may open new functionalization pathways for white phosphorus P4 .

Lifetime of Parahydrogen in Aqueous Solutions and Human Blood.

Molecular hydrogen has unique nuclear spin properties. Its nuclear spin isomer, parahydrogen (pH2 ), was instrumental in the early days of quantum mechanics and allows to boost the NMR signal by several orders of magnitude. pH2- induced polarization (PHIP) is based on the survival of pH2 spin order in solution, yet its lifetime has not been investigated in aqueous or biological media required for in vivo applications. Herein, we report longitudinal relaxation times (T1 ) and lifetimes of pH2 ( τPOC ) in methanol and water, with or without O2 , NaCl, rhodium-catalyst or human blood. Furthermore, we present a relaxation model that uses T1 and τPOC for more precise theoretical predictions of the H2 spin state in PHIP experiments. All measured T1 values were in the range of 1.4-2 s and τPOC values were of the order of 10-300 minutes. These relatively long lifetimes hold great promise for emerging in vivo implementations and applications of PHIP.

Why Do Five Ga+ Cations Form a Ligand-Stabilized [Ga5 ]5+ Pentagon and How Does a 5:1 Salt Pack in the Solid State?

The reaction of the Ga+ source [Ga(PhF)2 ]+ [Al(ORF )4 ]- with the neutral σ-donor ligand dmap (4-Me2 N-C6 H4 N) produces the unexpectedly large and fivefold positively charged cluster cation salt [Ga5 (dmap)10 ]5+ ([Al(ORF )4 ]- )5 . It includes a regular and planar Ga5 pentagon with strong metal-metal bonding. Additionally, the compound represents the first salt in which an ionic 1:5 packing is realized. We discuss the nature of this structure which results from the conversion of the non-bonding 4s2 lone-pair orbitals into fully Ga-Ga-bonding orbitals and the solid-state arrangement of the ions constituting the lattice as an almost orthohexagonal AX5 lattice, possibly the aristotype of any 5:1 salt.

The larmor frequency shift in magnetically heterogeneous media depends on their mesoscopic structure.

PURPOSE: Recent studies have addressed the determination of the NMR precession frequency in biological tissues containing magnetic susceptibility differences between cell types. The purpose of this study is to investigate the dependence of the precession frequency on medium microstructure using a simple physical model. THEORY: This dependence is governed by diffusion of NMR-visible molecules in magnetically heterogeneous microenvironments. In the limit of fast diffusion, the precession frequency is determined by the average susceptibility-induced magnetic field, whereas in the limit of slow diffusion it is determined by the average local phase factor of precessing spins. METHODS: The main method used is Monte Carlo simulation of isotropic suspensions of impermeable magnetized spheres. In addition, NMR spectroscopy was performed in aqueous suspensions of polystyrene microbeads. RESULTS: The precession frequency depends on the structural organization of magnetized objects in the medium. Monte Carlo simulations demonstrated a nonmonotonic transition between the regimes of fast and slow diffusion. NMR experiments confirmed the transition, but were unable to confirm its precise form. Results for a given pattern of structural organization obey a scaling law. CONCLUSION: The NMR precession frequency exhibits a complex dependence on medium structure. Our results suggest that the commonly assumed limit of fast water diffusion holds for biological tissues with small cells. Magn Reson Med 79:1101-1110, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Optimized synthesis and indium complex formation with the bifunctional chelator NODIA-Me.

The bifunctional chelator NODIA-Me holds promise for radiopharmaceutical development. NODIA-Me is based on the macrocycle TACN (1,4,7-triazacyclononane) and incorporates two additional methylimidazole arms for metal chelation and an acetic acid residue for bioconjugation. The original two step synthesis was less than optimal due to low yields and the requirement of semi-preparative RP-HPLC purifications. Here, the overall yield for the preparation of NODIA-Me was improved two- to five-fold via two synthetic routes using different protection/deprotection techniques. This way, it was possible (1) to prepare of NODIA-Me on multi-gram scale and (2) to avoid time-consuming HPLC purifications. Inspired by recent results with nat/68Ga3+, preliminary studies on the radiolabeling properties and complex formation of NODIA-Me with nat/111In3+ were performed. Quantitative radiochemical yields were achieved at ambient temperature providing molar activities of ∼30 MBq nmol-1, which could be increased to ∼240 MBq nmol-1 at 95 °C. At r.t., pH 5.5 was optimal for 111In-labeling, but quantitative yields were also achieved in the pH range from 5.5 to 8.2, when the reaction temperature was increased. Stability tests of 111In complexes in vitro revealed high kinetic stabilities in serum and ligand challenge experiments, which is a consequence of the formation of rigid 1 : 1 indium chelates as shown by NMR studies in solution. In summary, the new synthetic routes afford the BFC NODIA-Me in high yields and on large scale. Further, 111In complexation experiments broaden the scope of our chelating system for radiopharmaceutical applications.

Towards a Sustainable Synthesis of Oxymethylene Dimethyl Ether by Homogeneous Catalysis and Uptake of Molecular Formaldehyde.

Oxymethylene dimethyl ethers (OMEn ; CH3 (-OCH2 -)n O-CH3 , n=3-5) are a novel class of sustainable synthetic fuels, which are of increasing interest due to their soot-free combustion. Herein a novel anhydrous OMEn synthesis route is presented. Catalyzed by trimethyloxonium salts, dimethoxymethane takes up monomeric gaseous formaldehyde instantaneously and forms high purity OMEn at temperatures of 25-30 °C. This new anhydrous approach using molecular formaldehyde and catalytic amounts of highly active trimethyloxonium salts represents a promising new step towards a sustainable formation of OMEn emanating from CO2 and H2 .

Using the Lewis Acid Me3 Si-F-Al(ORF )3 To Prepare Phosphino-Phosphonium Cations with the Least-Coordinating Anion [(RF O)3 Al-F-Al(ORF )3 ].

By reaction of two equivalents of Me3 Si-F-Al(ORF )3 1 with an equimolar amount of PPh2 Cl, the salt [Ph2 P-PPh2 Cl]+ [(RF O)3 Al-F-Al(ORF )3 ]- 2 is prepared smoothly in 91 % yield (NMR, XRD). The synthesis of [Ph2 P-PPh3 ]+ [(RF O)3 Al-F-Al(ORF )3 ]- 3 is best achieved by a two-step reaction: first, two equivalents of 1 react with one PPh3 to give [Me3 Si-PPh3 ]+ [(RF O)3 Al-F-Al(ORF )3 ]- 4 (NMR, XRD), which, upon reaction with PPh2 Cl, yields pure 3 and Me3 SiCl (NMR, XRD). Typically, a stoichiometry of two equivalents of 1 with respect to one equivalent of the chloride donor should be used. Otherwise, the residual strong Lewis acidity of the [(RF O)3 Al-F-Al(ORF )3 ]- anion in the presence of the [F-Al(ORF )3 ]- anion-that forms with less than two equivalents of 1-leads to further chloride exchange reactions that complicate work-up. This route presents the easiest way to introduce the least-coordinating [(RF O)3 Al-F-Al(ORF )3 ]- anion into a system. We expect a wide use of this route in all areas, in which chloride-bond heterolysis in combination with very weakly coordinating anions is desirable. Additionally, we performed calculations on the bond dissociation mechanisms of [R2 P-PMe3 ]+ and the isoelectronic Me2 P-SiMe3 and Me2 Si-PMe3 in dependence of the solvent permittivity. These calculations show, especially for the neutral reference compounds, a heavy influence of the solvent on the dissociation mechanism, which is why we suggest investigating these properties in solution instead of gas phase.

An Investigation of the Symmetric and Asymmetric Cleavage Products in the System Aluminum Trihalide/1-Butylimidazole.

Mixtures of AlX3 (X=Cl, Br) with 1-butylimidazole (BuIm) in various ratios were investigated. The mixtures were characterized by multinuclear (1 H, 27 Al, 13 C, and 15 N) NMR, IR, and Raman spectroscopy and in part by single-crystal X-ray diffraction. Depending on the molar fraction x(AlBr3 ) of the AlBr3 -based mixtures, the cationic aluminum complexes [Al(BuIm)6 ]3+ and [AlBr2 (BuIm)4 ]+ , the neutral adduct [AlBr3 (BuIm)], as well as the anions Br- , [AlBr4 ]- , and [Al2 Br7 ]- could be identified as the products of the symmetric and asymmetric cleavage of dimeric Al2 Br6 . Furthermore, there are hints at the formation of [AlBr2 (BuIm)2 ]+ or related cations. Comparison of the AlBr3 /BuIm system with AlCl3 -based mixtures revealed the influence of the halide: In contrast to AlBr3 , the trication [Al(BuIm)6 ]3+ could not be detected as main product in a 1:6 mixture of AlCl3 and BuIm. Additionally, [AlCl3 (BuIm)] crystallizes from a mixture with x(AlCl3 )=0.60 at room temperature, whereas the corresponding AlBr3 -based mixture remains liquid even at +6 °C. Three AlBr3 -based mixtures are liquid at room temperature, whereas all other mixtures are solids with melting points between 46 and 184 °C. The three liquid mixtures exhibit medium to high viscosities (117 to >1440 mPa s), low conductivities (0.03-0.20 mS cm-1 ), but high densities (1.80-2.21 g cm-3 ). Aluminum could be successfully deposited from one of the neat Lewis acidic mixtures of the AlBr3 -based system.

Inhibiting Polysulfide Shuttle in Lithium-Sulfur Batteries through Low-Ion-Pairing Salts and a Triflamide Solvent.

The step-change in gravimetric energy density needed for electrochemical energy storage devices to power unmanned autonomous vehicles, electric vehicles, and enable low-cost clean grid storage is unlikely to be provided by conventional lithium ion batteries. Lithium-sulfur batteries comprising lightweight elements provide a promising alternative, but the associated polysulfide shuttle in typical ether-based electrolytes generates loss in capacity and low coulombic efficiency. The first new electrolyte based on a unique combination of a relatively hydrophobic sulfonamide solvent and a low ion-pairing salt, which inhibits the polysulfide shuttle, is presented. This system behaves as a sparingly solvating electrolyte at slightly elevated temperatures, where it sustains reversible capacities as high as 1200-1500 mAh g-1 over a wide range of current density (2C-C/5, respectively) when paired with a lithium metal anode, with a coulombic efficiency of >99.7 % in the absence of LiNO3 additive.

Effect of Dimethyl Carbonate on the Dynamic Properties and Ionicities of Ionic Liquids with [M(III) (hfip)4 ](-) (M=B, Al) Anions.

Several ionic liquids (ILs) comprising [B(hfip)4 ](-) [hfip=OCH(CF3 )2 ] or [Al(hfip)4 ](-) anions and imidazolium or ammonium cations were prepared and mixed with up to 270 mol % of dimethyl carbonate (DMC). The viscosities, conductivities, and self-diffusion constants of these mixtures and, where possible, of the neat ILs were measured and compared with common [NTf2 ](-) based ILs and their mixtures with DMC. A tremendous decrease of the viscosities and a likewise increase of the conductivities and diffusion constants can be achieved for all classes of ILs. However, the order of the conductivities is partially reversed in the diffusion data. This is probably due to the low dielectric constant of DMC and the, thus, favored ion pairing, as evidenced, for example, by the calculated ionicities. Altogether, our data show that the chemically robust, but high-melting and more viscous [B(hfip)4 ](-) ILs might be candidates for electrolytes when mixed with suitable molecular solvents.

Synthesis, crystal structure, and spectroscopy of the mixed-valent boroseleniteselenate B2Se3O10.

The first mixed-valent boroseleniteselenate B2Se3O10 was obtained as a colorless, hygroscopic compound from the reaction of boric acid (H3BO3) in concentrated selenic acid (H2SeO4) at 265 °C. H2SeO4 can be replaced by appropriate amounts of SeO2 and H2O2. The crystal structure was determined from single-crystal data (P21/c, Z = 4, a = 4.3466(2) Å, b = 7.0237(4) Å, c = 22.1460(9) Å, ß = 94.922(2)°, R1 = 0.036, wR2 = 0.096). It represents a new structure type that is characterized by a 3D net of BO4 tetrahedra, Se(VI)O4 tetrahedra, and trigonal-pyramidal Se(IV)O3 in a ratio of 2:1:2. (77)Se magic-angle-spinning NMR investigations confirm the mixed-valent character because the chemical shifts are found in the typical regions, i.e., 1278 and 1202 ppm for Se(IV) and 972 ppm for Se(VI). The vibrational spectra show the typical modes according to the present polyhedra. In addition, NMR and vibrational spectra of the closely related B2Se2O7 are presented.

A Janus-headed Lewis superacid: simple access to, and first application of Me3Si-F-Al(OR(F))3.

Upon reaction of gaseous Me3SiF with the in situ prepared Lewis acid Al(OR(F))3, the stable ion-like silylium compound Me3 Si-F-Al(OR(F))3 1 forms. The Janus-headed 1 is a readily available smart Lewis acid that differentiates between hard and soft nucleophiles, but also polymerizes isobutene effectively. Thus, in reactions of 1 with soft nucleophiles (Nu), such as phosphanes, the silylium side interacts in an orbital-controlled manner, with formation of [Me3Si-Nu](+) and the weakly coordinating [F-Al(OR(F))3](-) or [((F)RO)3Al-F-Al(OR(F))3](-) anions. If exchanged for hard nucleophiles, such as primary alcohols, the aluminum side reacts in a charge-controlled manner, with release of FSiMe3 gas and formation of the adduct R(H)O-Al(OR(F))3. Compound 1 very effectively initiates polymerization of 8 to 21 mL of liquid C4 H8 in 50 mL of CH2 Cl2 already at temperatures between -57 and -30 °C with initiator loads as low as 10 mg in a few seconds with 100% yield but broad polydispersities.

Synthesis and properties of the weakly coordinating anion [Me3 NB12 Cl11 ](-).

The weakly coordinating anion [Me3 NB12 Cl11 ](-) has been prepared by a simple two-step procedure. The anion [Me3 NB12 Cl11 ](-) is easily obtained in batches of up to 20 g by chlorination of the known [H3 NB12 H11 ](-) anion with SbCl5 at about 190 °C and subsequent N-methylation with methyl iodide. Starting from Na[Me3 NB12 Cl11 ], several synthetically useful salts with reactive cations ([NO](+) , [Ph3 C](+) , and [(Et3 Si)2 H](+) ) were prepared. Full spectroscopic (NMR, IR, Raman, TGA, MS) characterization and single-crystal X-ray diffraction studies confirmed the identity and purity of the products. The thermal, chemical, and electrochemical stability as well as the basicity of the [Me3 NB12 Cl11 ](-) anion is similar to that of the structurally related weakly coordinating 1-carba-closo-dodecaborate and closo-dodecaborate anions. The facile preparation of the [Me3 NB12 Cl11 ](-) anion and its ideal chemical and physical properties make it a cheap alternative to other classes of weakly coordinating anions.

Size matters! On the way to ionic liquid systems without ion pairing.

Several, partly new, ionic liquids (ILs) containing imidazolium and ammonium cations as well as the medium-sized [NTf2 ](-) (0.230 nm(3) ; Tf=CF3 SO3 (-) ) and the large [Al(hfip)4 ](-) (0.581 nm(3) ; hfip=OC(H)(CF3 )2 ) anions were synthesized and characterized. Their temperature-dependent viscosities and conductivities between 25 and 80 °C showed typical Vogel-Fulcher-Tammann (VFT) behavior. Ion-specific self-diffusion constants were measured at room temperature by pulsed-gradient stimulated-echo (PGSTE) NMR experiments. In general, self-diffusion constants of both cations and anions in [Al(hfip)4 ](-) -based ILs were higher than in [NTf2 ](-) -based ILs. Ionicities were calculated from self-diffusion constants and measured bulk conductivities, and showed that [Al(hfip)4 ](-) -based ILs yield higher ionicities than their [NTf2 ](-) analogues, the former of which reach values of virtually 100 % in some cases.From these observations it was concluded that [Al(hfip)4 ](-) -based ILs come close to systems without any interactions, and this hypothesis is underlined with a Hirshfeld analysis. Additionally, a robust, modified Marcus theory quantitatively accounted for the differences between the two anions and yielded a minimum of the activation energy for ion movement at an anion diameter of slightly greater than 1 nm, which fits almost perfectly the size of [Al(hfip)4 ](-) . Shallow Coulomb potential wells are responsible for the high mobility of ILs with such anions.